The syntax for constructing arrays is `Array{Type}(size1, size2, ...)`. You
are not passing any values for `size`, thus you are constructing an array
that has no indices (zero dimensions). The way to access it is `x[]`, i.e.
an indexing expression without any indices. All zero-dimensional arrays
have one element -- there is no way for it to have zero elements; a
zero-dimensional array is very similar to a scalar value.
Zero-dimensional arrays are confusing if you don't expect them; I assume
many people expect to obtain a one-dimensional array with zero elements
instead. (You can write `Vector{Int64}()` for this, or `Array{Int64}(0)`,
or Array{Int64,1}()`, or `Int64[]`.)
To add to the confusion, Julia supports "linear indexing", which allows you
to index arrays with fewer or more (!) indices than declared. If you use
fewer indices, then the last index can be larger than its declared bound;
if there are more, then the additional indices all need to have the value 1:
```Julia
x = Vector{Int}(10) # one dimension, ten elements
x[1,1] # this accesses the first element
x[1,1,1,1,1] # so does this
```
This allows you to write `x[1]` in your case, although `x` actually doesn't
have any indices.
Supporting zero-dimensional arrays is an important corner case.
Linear indexing is also important, but might use a different syntax in the
future to avoid confusion.
-erik
On Tue, Jun 7, 2016 at 9:47 PM, David Parks <[email protected]> wrote:
> Hi Mauro, thanks for the response!
> I get the logic behind an uninitialized array, but shouldn't such an array
> not return an iterable with 1 element of garbage? Why would it be
> initialized to having 1 random element and not 0?
>
> I would expect an empty constructor to do something reasonable. Perhaps it
> would be logical for these two statements to be equivalent (see bold lines
> below). I don't see the value of having a null constructor that generates
> an array that's iterable with exactly 1 element of garbage contents. Seems
> like a recipe for bugs. My bugs specifically, which is exactly what brought
> me to this topic. :)
>
> *julia> x = Array{Int64}()*
> 0-dimensional Array{Int64,0}:
> 2198389808
>
> julia> x[1]
> 2198389808
>
> julia> x[2]
> ERROR: BoundsError: attempt to access 0-dimensional Array{Int64,0}:
> 2198389808
> at index [2]
> in getindex at array.jl:282
>
> *julia> x=Array{Int64}(0)*
> 0-element Array{Int64,1}
>
> julia> x[1]
> ERROR: BoundsError: attempt to access 0-element Array{Int64,1}
> at index [1]
> in getindex at array.jl:282
>
>
>
>
>
>
>
>
--
Erik Schnetter <[email protected]>
http://www.perimeterinstitute.ca/personal/eschnetter/
